How to shrink your Virtual PC disk size on Mac OS X

If you use Microsoft Virtual PC with Windows XP Home on Mac OS X, you may find that your virtual PC's hard drive, or disk image, expands over time. In the year that I've been running Virtual PC 7 with Windows XP Home, my PC disk had grown from about 4 gigabytes to over 14 gigabytes, even though the only thing I installed on my PC was Firefox. (You'll typically find your Virtual PC disk as a file inside your user's Home folder, in Documents > Virtual PC List.)

You needn't loose disk space to this “dynamically expanding” disk, however. By following the instructions at Microsoft's Virtual PC Support website, I was able to shrink my virtual PC disk down to 5.8 gigabytes — a savings of 8 gigs!

For step-by-step instructions, see Microsoft's support article “How to reclaim disk space on a disk image in Virtual PC for Mac.”

For kicks, I ran the process twice, and saved a bit of space the second time around too, getting the disk image down to 5.33 GB.

Now, can you convert your newly-shrunk disk from a “dynamically expanding” disk image to “fixed,” so it doesn't creep up in size again? Bad news: you can't. When I ran Virtual PC's Virtual Disk Assistant and converted my 5.33 GB dynamically expanding disk to a fixed size disk, thinking I would prevent the disk from ballooning up again, it didn't create a fixed disk of 6 GB — on its own accord, it created a 15 GB disk. It did this even though I had only 4.8 GB of data on it. So I converted it back, from fixed to dynamic, and ended up at 5.36 GB.

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